An output of a solid-state laser such as a semiconductor laser is amplified and is used, for example, as a light source in a laser processing machine. It is known that, in an oscillation medium that oscillates a solid-state laser, an amount of heat emitted increases with an increase in the output thereof. Such an oscillation medium is a heat-emitting body, and a possibility exists that the oscillation medium may affect an operation of a device by diffusing heat to the surrounding thereof. Accordingly, it is necessary to cool the heat-emitting body.
As a technique of cooling the heat-emitting body, for example, techniques described in Patent Literature 1 and Patent Literature 2 are known.
Patent Literature 1 discloses a cooling device for a solid-state laser. The cooling device described in Patent Literature 1 includes a heat sink that is bonded to a solid-state laser oscillation element, a coolant tank that supplies a coolant, and a supply pipe that cause the coolant to circulate in the heat sink.
Patent Literature 2 discloses a cooling device for a magnetic resonance imaging (MRI) device. In the MRI device, a configuration in which liquid nitrogen, which is supplied as a cooling medium to a cryostat and made to circulate via a refrigerator, is employed to cool a gradient magnetic-field coil as a heat-emitting body. The liquid nitrogen is provided to cool the gradient magnetic-field coil in contact with the cryostat, has its temperature lowered by passing through a refrigerator, and flows through the cryostat again.
When the heat-emitting body is a laser medium in a laser oscillation device as described above, the amount of heat emitted reaches, for example, 0.25 KW per square centimeter. Accordingly, it is effective to spray the cooling medium directly onto the heat-emitting body so as to achieve a satisfactory cooling effect.
It is known that the cooling medium that is provided to cool the heat-emitting body and is evaporated is about 1% of the total cooling medium. That is, most of the cooling medium is not provided for cooling but is discharged. Accordingly, it is not economical to supply the cooling medium continuously and it is desirable to recover and reuse the cooling medium.